Emerald – May’s Only Birthstone
One of the most beautiful and rare gems found in nature is emerald. It is the most valuable variety of beryl and it is the only birthstone for May. Other beryls include, aquamarine, morganite and golden beryl (heliodore) as well as a few other lesser known varieties such as red beryl and a colorless variety.
Emerald’s Early Sources
Emeralds have been used in jewelry for thousands of years.
The earliest recorded accounts of emerald mining date back to the Cleopatra Mine in ancient Egypt. Other early sources include what is today Pakistan and Austria.
Everything changed though, when Spanish explorers arrived in the new world in the 16th century. Colombia quickly became known and recognized as the worlds premier emerald source; and has dominated the emerald market ever since.
Emeralds occur in an interesting range of modified greens. The perfect emerald color is described by GIA as “vivid, slightly bluish green.” This stunning color is rare indeed.
While beryl comes in many shades of green, to be classified as an emerald, the gem needs to be a medium or darker green. All other, lighter shades of green, are referred to as green beryl. While this might seem reasonable for practical purposes, scientifically, emerald is defined by its coloring agent. The American Gem Laboratory of New York, defines any green beryl colored by chromium and/or vanadium as emerald regardless of the tone. Although all emeralds contain iron as a trace element, a beryl variety that owes its green color to iron only is named green beryl.
Emeralds Current Mining Sources
Today, gem quality emeralds are found in a number of locations around the world. These include Brazil, Madagascar, Zambia, Mozambique, Nigeria, Zimbabwe, Tanzania, China, Afghanistan, India, Pakistan, Russia, Australia and the USA. Most recently a new find in Shakiso, Ethiopia has added new excitement to the industry by providing a new source for larger, high clarity gems.
Although emeralds can be found in a number of countries and on virtually every continent, the top three ranking locations for emerald are Colombia, Zambia and Brazil. While any emerald mine can produce fine color and high clarity stones, each source location tends to have its strengths and weaknesses. While Colombia is famous for its gorgeous, slightly bluish green gems, Zambian emerald is desired for its tendency to be slightly higher in clarity. Even so, this material can sometimes be a little too dark. On the other hand, top quality Zambian Emeralds are generally more affordable than Colombian emeralds of the same grade. The third most popular source of Emeralds is Brazil which produces a large volume of material. Most Brazilian emerald though is limited to medium and commercial grades.
One of the reasons for emeralds rarity is that its formation requires unusual geological conditions. These conditions also cause it to be a rather brittle gem. Due to its formation and the mining techniques commonly used, emerald tends to contain internal, and many case surface reaching fissures and cracks which can diminish its transparency. This means that high clarity stones are extremely rare. Due to its fissured and fractured nature, emerald’s transparency is almost always compromised.
Throughout its history, different types of oils, waxes and resins have been used to hide surface reaching breaks in order to enhance the clarity. The most common and practical treatment for emerald is clarity enhancement. This oiling and or filling, changes the appearance but not the structure. In the last twenty to thirty years, different types of polymer fillers have also been used. Clarity enhancement often dramatically affects the clarity and transparency. The price difference between treated and untreated, fine quality emeralds can be substantial.
Emerald is seldom heat treated. Irradiation (to improve color), is known, but the results are marginal at best. Use of polymer with dyes is also well-known. This must be disclosed as a color treatment and it significantly lowers the value of gems treated in this way. The use of polymer to fuse the pieces of low-grade emerald together in order to create larger pieces has been reported. These stones are considered as “composite” and must be distinguished from emerald for disclosure purposes.